1. Field
The present invention relates generally to video processing and, more specifically, to a Discrete Cosine Transform (DCT) performed on an N×M coefficient block in a system implementing a block-based, Moving Pictures Expert Group (MPEG)-like video coding standard.
2. Description
Many video coding standards, such as those developed by MPEG, are based on sample-to-frequency domain transitions and employ two-dimensional (2D) forward and inverse Discrete Cosine Transform (DCT) for converting raster data to frequency coefficient blocks, and for converting the compressed coefficient blocks back to raster data, respectively. The 2D DCT operation is defined by MPEG standards (e.g., ISO/IEC 13818-2, MPEG-2 coding standard: Video, ISO/IEC 14496-2, MPEG-4 coding standard, Visual) as a transformation of an 8×8 coefficient block and appears to be one the most time-consuming parts of a compressed video processing pipeline.
Some video coding standards (e.g., MPEG-4) impose additional restrictions on DCT precision compared to one defined by, for example, the Institute of Electrical and Electronics Engineers (IEEE) 1180-1990 standard (“IEEE Standard Specifications for the Implementation of 8×8 Inverse Discrete Cosine Transform”, 1997). Thus, the MPEG-4 standard treats the aforementioned standard requirements as necessary but not sufficient: “where arithmetic precision is not specified, such as in the calculation of the inverse DCT, the precision shall be sufficient so that significant errors do not occur in the final integer values.” For some coded video sequences, satisfactory results can be achieved if the DCT operation is implemented using single precision floating point arithmetic. At the same time, floating point operations are somewhat slower than integer instructions involved in fixed point calculations widely used in video processing systems to compute an 8×8 DCT.
Therefore, a need exists for the capability to provide high speed DCT execution while preserving the accuracy of single precision floating point operations.